Method and apparatus for coinjecting two thermoplastic materials

Abstract

Hot runner injection molding apparatus for coinjecting two thermoplastic materials sequentially through separate channels to form at least a two-layer sandwich material is provided. There is a valve means for instantaneously switching the flow of thermoplastic material from one channel to the other channel, the valve means preferably comprising a shuttle ball member.

What is claimed is: 
     
       1. A method of coinjecting two thermoplastic materials to form a two or more layer member using a hot runner injection molding machine with two separate channels, one channel for each material, each channel having an exit end that opens into a common exit cavity having a common gate entrance to an injection mold, the method comprising of: A. heating the thermoplastic materials in the two channels;   B. injecting material from the first channel through the common gate into the injection mold;   C. simultaneously forcing a valve member to seat itself in the exit end of the second channel to prevent intermixing of the two materials;   D. sequentially injecting material from the second channel through its exit end into the common exit cavity and into the common gate entrance;   E. simultaneously stopping the flow of material into the common exit cavity by forcing the valve member into the exit end of the first channel to seat itself therein; and   F. simultaneously cleaning the first material from the exit cavity and the gate entrance by forcing the valve member and the first material into the exit end of the first channel.   
     
     
       2. A process as defined in claim 1 in which one of the thermoplastic materials is a foamed material. 
     
     
       3. A process as defined in claim 1 in which the first injected thermoplastic material is a copolymer of ethylene and vinylacetate and the second injected thermoplastic material is polypropylene. 
     
     
       4. A method as defined in claim 1 in which a copolymer ethylene and vinylacetate is first injection molded into the mold and thereafter a polyolefin is injected into the mold to form a two-layer sandwich material. 
     
     
       5. A method as defined in claim 1 in which there are the further steps of: G. directing the first thermoplastic material into the mold to form a closure liner; and   H. directing and injecting a compatible material from the second channel into the mold to form a thermoplastic body for the closure liner resulting in a one-piece two-material closure.   
     
     
       6. A method as defined in claim 1 in which there are further steps of: I. directing and injecting the first thermoplastic material into a mold to form a closure liner; and   J. directing and injecting a dissimilar material from the second channel into the mold to form a thermoplastic body for the closure liner, resulting in a two-piece two-material closure.   
     
     
       7. A method as defined in claim 1 in which the valve member is a shuttle ball. 
     
     
       8. A method as defined in claim 1 in which the valve member is a swing gate that pivots from a fixed point in the common exit cavity where the end of the gate is attached to swing from one exit end to the other exit end of the channels. 
     
     
       9. A method as defined in claim 1 in which there is provided the further steps of: K. directing the first thermoplastic material into the mold to form an outer layer of the final article;   L. directing the injection of a second foamed thermoplastic core material from the second channel into the mold to form a foamed core article; and   M. directing the first thermoplastic material into the mold to form a layer and seal off the foamed material at the gate and form the final article.   
     
     
       10. A hot runner injection molding apparatus for coinjecting two thermoplastic materials sequentially through separate channels to form at least a two-layer sandwich material, each channel being independently heated and each channel having an exit end in communication with a common exit cavity with a common gate entrance to a forming mold, there being valve means for instantaneously switching flow of thermoplastic material from one channel to the other channel without intermixing materials from the two channels, the valve means being disposed within the common exit cavity between the exit ends of the channels, the valve means comprising a shuttle member that removes residual material from the common gate entrance and seats in the exit end of one channel as material flows through the exit end of the other channel into the common exit cavity and through the common gate whereby the materials are sequentially injected into the mold. 
     
     
       11. An apparatus as defined in claim 10 in which there is provided means for independently heating the two channels located between and around the two channels. 
     
     
       12. An apparatus as defined in claim 10 in which the shuttle member is a ball. 
     
     
       13. An apparatus as defined in claim 10 in which the shuttle member is a swing gate, the swing gate having a first end portion integrally connected to a central portion of the common exit cavity, the swing gate having another end portion that pivots at the first end portion to swing from the exit end of one channel to the other channel of the other channel end. 
     
     
       14. An apparatus as defined in claim 10 in which the forming mold is an injection mold. 
     
     
       15. An apparatus as defined in claim 10 in which there is further provided means for molding the two thermoplastic materials into a two-piece closure, the one material forming the closure shell and the other dissimilar material forming a liner therefor. 
     
     
       16. An apparatus as defined in claim 10 in which there is further provided a means for molding the two thermoplastic materials into a one-piece closure, the one material forming the closure shell or body and the compatible material forming the liner thereof. 
     
     
       17. An apparatus as defined in claim 10 in which there is further means for making a foam core comprising means for extruding a skin of the first thermoplastic material and means for providing a foam interior of the second thermoplastic material inside of the skin material to form a foam core, resulting in sink free articles.